McBell
Resident Sourpuss
A March paper in Trends in Genetics holds the unorthodox explanation: The gene became part of the smelt genome through a direct horizontal transfer from a herring. It wasn’t through hybridization, because herring and smelt can’t crossbreed, as many failed attempts have shown. The herring gene made its way into the smelt genome outside the normal sexual channels.
https://www.quantamagazine.org/dna-jumps-between-animal-species-no-one-knows-how-often-20210609/